The pressure at which typical gas distribution systems supply gas may vary according to the demands placed on the system, the climate, the source of supply, and/or other factors. However, most end-user facilities equipped with gas appliances such as furnaces, ovens, etc., require the gas to be delivered in accordance with a predetermined pressure, and at or below a maximum capacity of a gas regulator. Therefore, gas regulators are implemented into these distribution systems to ensure that the delivered gas meets the requirements of the end-user facilities. Conventional gas regulators generally include a closed-loop control actuator for sensing and controlling the pressure of the delivered gas.
In addition to a closed loop control, some conventional gas regulators include a relief valve. The relief valve is adapted to provide over pressure protection when the regulator or some other component of the fluid distribution system fails, for example. Accordingly, in the event the delivery pressure rises above a predetermined threshold pressure, the relief valve opens to exhaust at least a portion of the gas to the atmosphere, thereby reducing the pressure in the system.
FIGS. 1 and 1A depict one conventional gas regulator 10. The regulator 10 generally comprises an actuator 12 and a regulator valve 14. The regulator valve 14 defines an inlet 16 for receiving gas from a gas distribution system, for example, and an outlet 18 for delivering gas to an end-user facility such as a factory, a restaurant, an apartment building, etc. having one or more appliances, for example. Additionally, the regulator valve 14 includes a valve port 36 disposed between the inlet and the outlet. Gas must pass through the valve port 36 to travel between the inlet 16 and the outlet 18 of the regulator valve 14.
The actuator 12 is coupled to the regulator valve 14 to ensure that the pressure at the outlet 18 of the regulator valve 14, i.e., the outlet pressure, is in accordance with a desired outlet or control pressure. The actuator 12 is therefore in fluid communication with the regulator valve 14 via a valve mouth 34 and an actuator mouth 20. The actuator 12 includes a control assembly 22 for sensing and regulating the outlet pressure of the regulator valve 14. Specifically, the control assembly 22 includes a diaphragm 24, a piston 32, and a control arm 26 having a valve disc 28. The conventional valve disc 28 includes a generally cylindrical body 25 and a sealing insert 29 fixed to the body 25. The valve body 25 may also include a circumferential flange 31 integrally formed therewith, as depicted in FIG. 1A. The diaphragm 24 senses the outlet pressure of the regulator valve 14. The control assembly 22 further includes a control spring 30 in engagement with a top-side of the diaphragm 24 to offset the sensed outlet pressure. Accordingly, the desired outlet pressure, which may also be referred to as the control pressure, is set by the selection of the control spring 30.
The diaphragm 24 is operably coupled to the control arm 26, and therefore, the valve disc 28 via the piston 32, controls the opening of the regulator valve 14 based on the sensed outlet pressure. For example, when an end user operates an appliance, such as a furnace, for example, that places a demand on the gas distribution system downstream of the regulator 10, the outlet flow increases, thereby decreasing the outlet pressure. Accordingly, the diaphragm 24 senses this decreased outlet pressure. This allows the control spring 30 to expand and move the piston 32 and the right-side of the control arm 26 downward, relative to the orientation of FIG. 1. This displacement of the control arm 26 moves the valve disc 28 away from the valve port 36 to open the regulator valve 14. FIG. 1A depicts the valve disc 28 in a normal, open operating position. So configured, the appliance may draw gas through the valve port 36 toward the outlet 18 of the regulator valve 14.
In the conventional regulator 10, the control spring 30 inherently generates less force as it expands towards an uncompressed length when displacing the control arm 26 to open the valve port 36. Additionally, as the control spring 30 expands, the diaphragm 24 deforms, which increases the area of the diaphragm 24. The decreased force supplied by the control spring 30 and the increased area of the diaphragm 24 in this operational scenario combine to create a regulator response wherein the force provided by the control spring 30 cannot adequately balance the force generated by the diaphragm 24 thereby resulting in an outlet control pressure that is less than that originally set by the user. This phenomenon is known as “droop.” When “droop” occurs, the outlet pressure decreases below its set control pressure and the regulator 10 may not function as intended.
In the conventional regulator 10 depicted in FIG. 1, the control assembly 22 further functions as a relief valve, as mentioned above. Specifically, the control assembly 22 also includes a relief spring 40 and a release valve 42. The diaphragm 24 includes an opening 44 through a central portion thereof and the piston 32 includes a sealing cup 38. The relief spring 40 is disposed between the piston 32 and the diaphragm 24 to bias the diaphragm 24 against the sealing cup 38 to close the opening 44, during normal operation. Upon the occurrence of a failure such as a break in the control arm 26, the control assembly 22 is no longer in direct control of the valve disc 28 and inlet flow will move the valve disc 28 will move into an extreme open position. This allows a maximum amount of gas to flow into the actuator 12. Thus, as the gas fills the actuator 12, pressure builds against the diaphragm 24 forcing the diaphragm 24 away from the sealing cup 38, thereby exposing the opening 44. The gas therefore flows through the opening 44 in the diaphragm 24 and toward the release valve 42. The release valve 42 includes a valve plug 46 and a release spring 54 biasing the valve plug 46 into a closed position, as depicted in FIG. 2. Upon the pressure within the actuator 12 and adjacent the release valve 42 reaching a predetermined threshold pressure, the valve plug 46 displaces upward against the bias of the release spring 54 and opens, thereby exhausting gas into the atmosphere and reducing the pressure in the regulator 10.
When selecting a regulator for use in a particular application, technicians are charged with the task of maximizing flow capacity at the set control pressure while minimizing the amount of gas exhausted to the atmosphere under failure conditions. Typically, this task is accomplished by designing or selecting various aspects of the regulator 10, such as the valve port, to afford some compromise between these competing interests. In order to limit the amount of gas released to the atmosphere by the relief valve, technicians often choose the smallest port available to meet the required flow capacity.